The present invention relates to an installation and to a method for on-site preparation of a precursor of an explosive emulsion constituted by a reverse emulsion (water-in-oil).
In order to limit risks linked to transport, explosive precursors are manufactured on-site by emulsifying a concentrated aqueous phase, in particular supersaturated with nitrates constituting an oxidant, in an oily phase containing a surfactant and constituting a mixture of fuels.
The aqueous phase is typically prepared by dissolving nitrates of ammonium and/or sodium and/or calcium in water, to which there are additives for encouraging gasification and additives for adjusting the pH of the aqueous phase. Because of the high concentration of nitrates (in a proportion by weight of approximately 80%-82% for 18%-20% of water) and in order to facilitate dissolving them, the water is heated to a temperature of at least 65° C. (degrees Celsius).
The oily phase is composed of a mixture of various vegetable or mineral fats and surfactants. More particularly, the oily phase obtained by mixing fresh or recycled mineral oils such as paraffin oils and fuel oil, preferably in a proportion by weight of 50/50 to 80/20 with a quantity of surfactant in a proportion of 10% to 30% of the total of the oily phase.
In order to encourage mixing and reduce the temperature difference between the aqueous phase and the oily phase before mixing them into the emulsion, the oily phase is heated to approximately 40° C.-90° C., preferably 50° C.-70° C.
In order to mix and produce the emulsion, a low viscosity premix is prepared in a tank containing stirrer means. Because of its low viscosity, this premix has insufficient stability and its consistency is not appropriate for its subsequent use in preparing the explosive. For this reason, the viscosity of the premix is increased with the aid of a shear device in order to obtain an emulsion with higher viscosity.
Because of the specific nature of the emulsion constituting the explosive precursor, it is advantageously manufactured on-site in a modular installation that is transportable and that can be set up on-site in containers. In order to facilitate transport, the elements allowing the precursor manufacturing method to be carried out are transported in containers. The arrangement of those elements in the containers is such that as few operations as possible are needed when setting up the installation.
More particularly, the present invention concerns a modular installation for carrying out a method of manufacturing an explosive emulsion precursor constituted by a water-in-oil reverse emulsion, the method comprising:
a) a step of preparing an aqueous phase by dissolving nitrates in water and heating;
b) a step of preparing an oily phase by mixing components comprising at least one vegetable and/or mineral fat and a surfactant, and heating; and
c) a step of preparing said emulsion by mixing said aqueous phase into said oily phase. Said emulsion is subsequently rendered explosive by adding and mixing chemical reagents such as a solution of sodium nitrite and/or solid sensitizing agents such as glass microspheres in on-site manufacturing units just before use as an explosive for introducing into blast holes.
U.S. Pat. No. 4,526,633 and GB 2 126 910 disclose small mobile installations, in particular in the form of a truck carrying a platform supporting tanks in particular respectively for storing the aqueous phase and the oily phase, together with means for manufacturing an explosive in situ by mixing said aqueous and oily phases and other components. Firstly, those small installations have small production capacity, and secondly they are relatively dangerous because oxidant (aqueous phase) and fuel (oily phase) are transported close to each other with no safe physical separation of the tanks. Further, the tank containing said aqueous phase needs to be thermally insulated, in particular in order to prevent crystallization of said aqueous phase. Finally, in those methods, an explosive precursor containing only the mixture of aqueous phase and oily phase but without sensitizing agent is not specifically isolated. That results in a method and a device that are relatively complex and expensive to implement.
A modular installation is known from the prior art, essentially composed of two juxtaposed containers that are large (having a length of approximately 12.2 meters (m) (i.e. 40 feet)) and that communicate via one of their longitudinal faces. One of the containers includes dissolution tanks for preparing the aqueous phase and a heater separated by a partition. The other container includes tanks for preparing the oily phase and the reverse emulsion and also a separate electrical unit. Thus, the three steps in preparing the emulsion occur in a common container. The fact that the three steps in preparing the emulsion occur in the same container gives rise to risks as regards the safety of the site and/or of operators in the event of an incident and/or damage.
In addition, transporting containers of such a large size is not easy. It is in fact desirable to be able to transport containers that have already been fitted out, because if the installation is assembled on site, it requires qualified personnel to be mobilized, which gives rise to additional costs, in particular if optional elements are to be added subsequently.
The term “container” as used herein means the steel boxes that are used to transport goods and that have standardized features, in particular in accordance with standards ISO 668 and ISO 1496.